Turbidity sensors are commonly used in dishwashers to sense the amount of food particles in the water. The sensors typically are submerged in the water from the wash chamber. The wash water is recirculated during the wash operation until it reaches a predetermined level of turbidity wherein the food particles exceed a desired level. This dirty water is then discharged and replaced with fresh, clean water.
The turbidity sensors typically include an infrared transmitter and an infrared receiver or sensor mounted in a plastic housing. A problem associated with convention turbidity sensors is the accuracy of the output signal. The housing has a tendency to accumulate small bubbles while the water flows over the housing. When the bubbles collect on or travel over the area of the housing through which the infrared signal is traveling, the output signal of the sensor is adversely affected by this bubble-induced noise.
There have been various attempts to minimize or eliminate the problems associated with bubbles on the turbidity sensor housing, though none of the solutions have proved sufficiently effective. These prior art efforts include increasing the water fill level to reduce bubbles in the water; increasing the water velocity; turning the sensor 90° relative to the water flow; adding baffles in the water flow to change the turbulence thereof; polishing the surface of the sensor with a compound; using hot air to re-flow and smooth the surface; and coating the sensor with super glue.
Accordingly, a primary objective of the present invention is the provision of an improved turbidity sensor which is flame treated to reduce the adverse bubble effect on the sensor output.
Another objective of the present invention is the provision of a method of manufacturing a turbidity sensor wherein the housing of the sensor is treated to affect the surface energy of the housing.
A further objective of the present invention is the provision of a method of manufacturing a turbidity sensor wherein the plastic housing is subjected to a single and rapid application of heat to the surface during the manufacturing process.
A further objective of the present invention is the provision of an improved turbidity sensor having a reduction in bubble-induced noise in the output signal of the turbidity sensor.
Another objective of the present invention is the provision of an improved turbidity sensor which is economical to manufacture and accurate in use.
These and other objectives will be apparent from the following description of the invention.